This invention relates to abnormal event monitors, and more particularly to dynamic signal monitors for parts of operating plants that are not readily accessible for inspection.
Some plants are designed to operate for extended periods, such as nuclear power plants. Inspection is virtually impossible in many of these plants without shutting down. Yet it would be desirable to continually seek out potential problems, analyze them as to severity and indicate what action should be taken.
Loose parts in a nuclear power plant can cause a variety of problems. In view of this, loose parts monitoring of nuclear power plants has become common practice. A typical loose part monitor is disclosed in U.S. Pat. No. 3,860,481. Monitoring is accomplished on-line by picking up impact energy of a loose part by a suitable sensor attached to it, and detecting the energy at the resonant frequency of the loose part. The output of the sensor is analyzed as to the rate and the energy with which impact of the loose part occurs. However, this only indicates that a part being monitored has become loose, and does not provide information as to other conditions that may indicate a malfunction, or that would indicate a potential malfunction. For free and loose part detection, still other techniques have been developed as disclosed in U.S. Pat. Nos. 3,681,976 and 3,534,589.
Nondestructive testing of pressure vessels, and the like, have been devised based on monitoring and analyzing stress waves as disclosed in U.S. Pat. No. 3,545,262, and based on ultrasonic pulsing techniques as disclosed in U.S. Pat. No. 3,857,052. Stress wave analysis is not, however, suitable for on-line monitoring, and ultrasonic pulsing techniques are limited to applications where an ultrasonic transducer can be positioned or caused to be positioned from a remote console.
What is required is a system for continuously monitoring a plant on-line for anomalous behavior in which the monitor becomes part of the plant instrumentation and requires no operator action unless and anomalous condition is detected. Such a monitoring system can decrease operating costs by preventive maintenance techniques.
In any particular system there will be a number of key parameters which can be easily monitored, such as temperature and pressure. However, it would not be sufficient to monitor these parameters as they would, in general, indicate only when an alarm condition is reached, and provide no opportunity to diagnose potential malfunction due to impending failure of some part, such as a pump or motor.
It has been recognized that operating machinery will have characteristic vibrations which will vary if the machinery is not operating properly or if some part begins to deteriorate. See for example U.S. Pat. Nos. 3,641,550 and 3,758,758. For effective monitoring, the vibration signals of interest must be identifiable above the background noise, which means that a baseline (background) record of the sensor signal must be made to serve as a reference for comparison purposes later. Both the linear vibration and nonlinear loose parts signals must be detected and identified above the background noise. For cost effectiveness, the sensors employed should be passive, rather than active as in the ultrasonic system disclosed in U.S. Pat. No. 3,753,852 for monitoring vibrations in a nuclear reactor. However, the use of passive sensors makes the background noise problem more severe.
Monitoring the vibration energy of a cutting tool and comparing it with a reference has been recognized as an effective way of determining wear for the purpose of determining the optimum time to change the tool. See for example U.S. Pat. Nos. 3,694,637 and 3,841,149. But monitoring a single tool is not the same problem as monitoring an operating plant. Plants usually have complex vibrational patterns due to various components operating independently. To complicate things even more, some components operate independently and unsynchronized, and some even operate intermittently.
The development of programmed digital computers has made monitoring systems for complex operating plants feasible, as disclosed in U.S. Pat. No. 3,142,820. In that monitoring system, variables of the plant are monitored for comparison with operating limits. That will permit control of the plant, as by computing new set points for factors controlling the variable, and will, of course, permit alarm conditions to be detected and announced. The problem is that a failing component may, in the process, be overloaded to cause a complete break down. It would be desirable to monitor the vibrations of key components and points in the plant, not for control as disclosed in U.S. Pat. No. 3,710,082 in a vibration testing environment, but to find potential malfunctions, draw some conclusions as to their severity, and then indicate to the operator what action he should take for preventive maintenance.